27,824 research outputs found
Thermal surveillance of Cascade Range volcanoes using ERTS-1 multispectral scanner, aircraft imaging systems, and ground-based data communication platforms
A combination of infrared images depicting areas of thermal emission and ground calibration points have proved to be particularly useful in plotting time-dependent changes in surface temperatures and radiance and in delimiting areas of predominantly convective heat flow to the earth's surface in the Cascade Range and on Surtsey Volcano, Iceland. In an integrated experiment group using ERTS-1 multispectral scanner (MSS) and aircraft infrared imaging systems in conjunction with multiple thermistor arrays, volcano surface temperatures are relayed daily to Washington via data communication platform (DCP) transmitters and ERTS-1. ERTS-1 MSS imagery has revealed curvilinear structures at Lassen, the full extent of which have not been previously mapped. Interestingly, the major surface thermal manifestations at Lassen are aligned along these structures, particularly in the Warner Valley
Soil Moisture Workshop
The Soil Moisture Workshop was held at the United States Department of Agriculture National Agricultural Library in Beltsville, Maryland on January 17-19, 1978. The objectives of the Workshop were to evaluate the state of the art of remote sensing of soil moisture; examine the needs of potential users; and make recommendations concerning the future of soil moisture research and development. To accomplish these objectives, small working groups were organized in advance of the Workshop to prepare position papers. These papers served as the basis for this report
Decay rate and other properties of the positronium negative ion
A new method for detecting the positronium minus ion is described, and the possibility of a long positronium mean free path in a solid is discussed
The Narrow-band Ultraviolet Imaging Experiment for Wide-field Surveys (NUVIEWS)-I: Dust scattered continuum
We report on the first results of the Narrow-band Ultraviolet Imaging
Experiment for Wide-field Surveys (NUVIEWS), a sounding rocket experiment
designed to map the far-ultraviolet background in four narrow bands. This is
the first imaging measurement of the UV background to cover a substantial
fraction of the sky. The narrow band responses (145, 155, 161, and 174 nm, 7-10
nm wide) allow us to isolate background contributions from dust-scattered
continuum, H2 fluorescence, and CIV 155 nm emission. In our first flight, we
mapped one quarter of the sky with 5-10 arcminute imaging resolution. In this
paper, we model the dominant contribution of the background, dust-scattered
continuum. Our data base consists of a map of over 10,000 sq. degrees with 468
independent measurements in 6.25 by 6.25 sq. degree bins. Stars and
instrumental stellar halos are removed from the data. We present a map of the
continuum background obtained in the 174 nm telescope. We use a model that
follows Witt, Friedman, and Sasseen (1997: WFS) to account for the
inhomogeneous radiation field and multiple scattering effects in clouds. We
find that the dust in the diffuse interstellar medium displays a moderate
albedo (a=0.55+/-0.1) and highly forward scattering phase function parameter
(g=0.75+/-0.1) over a large fraction of the sky, similar to dust in star
forming regions. We also have discovered a significant variance from the model.Comment: 16 pages, 3 ps figures, submitted to Astrophysical Journal Letter
The exp-log normal form of types
Lambda calculi with algebraic data types lie at the core of functional
programming languages and proof assistants, but conceal at least two
fundamental theoretical problems already in the presence of the simplest
non-trivial data type, the sum type. First, we do not know of an explicit and
implemented algorithm for deciding the beta-eta-equality of terms---and this in
spite of the first decidability results proven two decades ago. Second, it is
not clear how to decide when two types are essentially the same, i.e.
isomorphic, in spite of the meta-theoretic results on decidability of the
isomorphism.
In this paper, we present the exp-log normal form of types---derived from the
representation of exponential polynomials via the unary exponential and
logarithmic functions---that any type built from arrows, products, and sums,
can be isomorphically mapped to. The type normal form can be used as a simple
heuristic for deciding type isomorphism, thanks to the fact that it is a
systematic application of the high-school identities.
We then show that the type normal form allows to reduce the standard beta-eta
equational theory of the lambda calculus to a specialized version of itself,
while preserving the completeness of equality on terms. We end by describing an
alternative representation of normal terms of the lambda calculus with sums,
together with a Coq-implemented converter into/from our new term calculus. The
difference with the only other previously implemented heuristic for deciding
interesting instances of eta-equality by Balat, Di Cosmo, and Fiore, is that we
exploit the type information of terms substantially and this often allows us to
obtain a canonical representation of terms without performing sophisticated
term analyses
Modification of turbulent transport with continuous variation of flow shear in the Large Plasma Device
Continuous control over azimuthal flow and shear in the edge of the Large
Plasma Device (LAPD) has been achieved using a biasable limiter which has
allowed a careful study of the effect of flow shear on pressure-gradient-driven
turbulence and transport in LAPD. LAPD rotates spontaneously in the ion
diamagnetic direction (IDD); positive limiter bias first reduces, then
minimizes (producing a near-zero shear state), and finally reverses the flow
into the electron diamagnetic direction (EDD). Degradation of particle
confinement is observed in the minimum shearing state and reduction in
turbulent particle flux is observed with increasing shearing in both flow
directions. Near-complete suppression of turbulent particle flux is observed
for shearing rates comparable to the turbulent autocorrelation rate measured in
the minimum shear state. Turbulent flux suppression is dominated by amplitude
reduction in low-frequency (kHz) density fluctuations. An increase in
fluctuations for the highest shearing states is observed with the emergence of
a coherent mode which does not lead to net particle transport. The variations
of density fluctuations are fit well with power-laws and compare favorably to
simple models of shear suppression of transport.Comment: 10 pages, 5 figures; Submitted to Phys. Rev. Let
Detecting many-body entanglements in noninteracting ultracold atomic fermi gases
We explore the possibility of detecting many-body entanglement using
time-of-flight (TOF) momentum correlations in ultracold atomic fermi gases. In
analogy to the vacuum correlations responsible for Bekenstein-Hawking black
hole entropy, a partitioned atomic gas will exhibit particle-hole correlations
responsible for entanglement entropy. The signature of these momentum
correlations might be detected by a sensitive TOF type experiment.Comment: 5 pages, 5 figures, fixed axes labels on figs. 3 and 5, added
reference
On the Perturbations of Viscous Rotating Newtonian Fluids
The perturbations of weakly-viscous, barotropic, non-self-gravitating,
Newtonian rotating fluids are analyzed via a single partial differential
equation. The results are then used to find an expression for the
viscosity-induced normal-mode complex eigenfrequency shift, with respect to the
case of adiabatic perturbations. However, the effects of viscosity are assumed
to have been incorporated in the unperturbed (equilibrium) model. This paper is
an extension of the normal-mode formalism developed by Ipser & Lindblom for
adiabatic pulsations of purely-rotating perfect fluids. The formulas derived
are readily applicable to the perturbations of thin and thick accretion disks.
We provide explicit expressions for thin disks, employing results from previous
relativistic analyses of adiabatic normal modes of oscillation. In this case,
we find that viscosity causes the fundamental p- and g- modes to grow while the
fundamental c-mode could have either sign of the damping rate.Comment: Accepted for publication by The Astrophysical Journal. 11 pages, no
figure
Path Integrals, Density Matrices, and Information Flow with Closed Timelike Curves
Two formulations of quantum mechanics, inequivalent in the presence of closed
timelike curves, are studied in the context of a soluable system. It
illustrates how quantum field nonlinearities lead to a breakdown of unitarity,
causality, and superposition using a path integral. Deutsch's density matrix
approach is causal but typically destroys coherence. For each of these
formulations I demonstrate that there are yet further alternatives in
prescribing the handling of information flow (inequivalent to previous
analyses) that have implications for any system in which unitarity or coherence
are not preserved.Comment: 25 pages, phyzzx, CALT-68-188
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